In general, polyamide resins such as nylons have excellent mechanical characteristics and excellent abrasion resistance. Therefore, they have been widely used for sliding parts such as a door-checking lever for an automobile, gears, and cam bearings. Plastic materials employed for this kind of application are usually required to meet conditions in terms of abrasion proof, impact strength for example. However, conventional polyamide resins exhibit the above characteristics only to an unsatisfactory extent. For this reason, commercially available polyamide resin compositions usually contain various kinds of additives such as wollastonites; elastomers; modified high-density polyethylenes; and Kevlar fibers, as disclosed in Japanese Patent No. 3417600 (corresponding to U.S. Pat. No. 5,583,177A) and Japanese Application Publication No. 05(1993)-65328 (corresponding to U.S. Pat. No. 6,113,832A).
A polyamide resin composition, which is disclosed in Japanese Patent No. 3417600, contains: (A) 85 to 95 parts by weight of a polyamide resin; (B) 5 to 15 parts by weight of a wollastonite; (C) 3 to 10 parts by weight, to 100 parts by the total weight of ingredients (A) and (B), of a styrene copolymer modified with at least one modifier selected from a group consisting of unsaturated carboxylic acids and/or unsaturated dicarboxylic anhydrides; and (D) 0.5 to 5 parts by weight, to 100 parts by the total weight of ingredients (A) and (B), of a high-density polyethylene modified with at least one modifier selected from the group consisting of unsaturated carboxylic acids and unsaturated dicarboxylic anhydrides, the high-density polyethylene having a weight average molecular weight of 50,000 to 400,000. A polyamide resin composition, which is disclosed in Japanese Publication No. 05(1993)-65328, contains an additive such as Kevlar fibers to nylon.
However, sliding parts, which is made from a conventional polyamide resin composition such as above, on occasions exhibits, at a high moisture atmosphere, an increased distortion amount of materials consisting the polyamide resin composition. When this type of polyamide resin composition is employed for a door-checking lever for an automobile, such distortion of materials consisting the polyamide resin composition may on occasions result in increasing a degree of operation force required for opening and closing a door. In such circumstances, the door-checking lever for an automobile may not meet a desired level of functions. Further, sliding parts, which are made from a conventional polyamide resin composition containing, therein, Kevlar fibers that generally cost high, are likely to be required to reduce manufacturing costs.
The present invention has been made in view of the above circumstances, and provides sliding parts employing a polyamide resin composition which is capable of providing excellent friction proof, excellent impact strength, excellent form stability against moisture absorption or at a high humid temperature, and is capable of reducing a manufacturing cost thereof.